Dispersion and chemical composition of Athena II rocket plumes: Model simulations versus in-situ aircraft measurements
During launches, rockets release large amounts of gases and particles into the atmosphere. For Solid-fuelled Rocket Motor (SRM), launches often result into the release of chemically active radicals (chlorine radicals, nitrogen oxides,…), and alumina particles into the stratosphere. In-situ aircraft measurements within SRM plume wakes have shown that, as a result, ozone is largely destroyed within plumes because concentrations of ozone-destroying chlorine radical concentrations can be several orders of magnitude higher in the plume than in the undisturbed atmosphere [Ross et al., 1997]. This transient effect lasts for several hours or as long the exhaust plume is not completely mixed with the ambient air. We present here numerical simulations of the evolution of SRM plumes and of their chemical compositions in the stratosphere. The focus is on the short-term effect on ozone. The evolution can be divided into two phases: near field phase (jet emerging from the nozzle exit) and far field phase. These two phases are characterised by different driving physical (rocket fluid dynamics versus atmospheric dynamics) and chemical (high temperature versus low temperature chemistry) processes. The temporal and spatial scales are also very different. The spatial scale of interest for the near field plume is of the order of a meter whereas the scales in the far field plume range from several meters to tens of kilometers typically. Exhausts spend about a second in the near-field plume whereas the far-field plume lasts several hours typically. No models are able to treat simultaneously, on one hand, very high temperature chemistry (including afterburning) and jet dynamics and, on the other hand, low temperature (ambient temperature) chemistry and relevant atmospheric dynamical processes. Therefore, we use two specific plume chemistry models for each phase with the results of the near-field plume model being used as inputs for the far-field plume model. The near-field plume simulations are compared to previous model calculations and the model- calculated chemical evolution of the far-field plume is evaluated against in-situ aircraft measurements carried out in Athena rocket plumes during the ACCESS (Atmospheric Chemistry of Combustion Emissions Near the Tropopause) campaigns [Popp et al., 2002]. The model- calculated dispersion rate of the far-field plume is also evaluated against plume diffusion rates derived from videos, photos, lidar measurements, as compiled by Smith et al. review . We finely analyse the fate of reactive chlorine and nitrogen in the plume and the possible role of heterogeneous chemistry on alumina particles.